Chemical reactionssc130chc.weebly.com/uploads/7/1/6/9/71691711/ps10_10... · 2019. 11. 11. · 5.1Chemical equations Every time you light a candle, bake a cake, take a breath or even

Chemical reactions 5

HAVE YOU EVER WONDERED…• what makes a bullet

explode?

• how a candle stays alight?

• where a battery gets its energy from?

• why you put milk in the fridge?

• use word and formula equations to represent chemical reactions

• predict the products of different types of simple chemical reactions

• describe how chemistry can be used to produce a range of useful substances such as fuels, metals and pharmaceuticals

• explain the effect of a range of factors including temperature, surface area, concentration, agitation and catalysts on the rate of chemical reactions.

After completing this chapter students should be able to:

141

AC-Sci-SB10-Ch05-FINAL.indd 141 11/10/11 10:48 AM

Chemical equations5.1Every time you light a candle, bake a cake, take a breath or even think, you start a chemical reaction. You may not always notice them, but chemical reactions are going on constantly around you and inside you. By understanding how chemical reactions work, scientists are able to use and control chemical reactions to improve our quality of life. Chemists have developed their own way of describing and explaining what happens during a chemical reaction. They do this by writing chemical equations.

What is a chemical equation?Chemical equations are one of the most basic tools for describing what happens during a chemical reaction. A chemical equation can communicate detailed information about any chemical reaction in a single line. The general structure of a chemical equation is:

reactants → products

where the arrow (→) means ‘rearrange to form’.

Word and formula equationsReplacing the reactants and products with their chemical names gives a word equation. For example, when calcium carbonate (CaCO

3) reacts with sulfuric acid (H

2SO

4), it produces calcium

sulfate (CaSO4), water (H

2O) and carbon dioxide gas (CO

2). In this

reaction, you have:

Reactants = calcium carbonate, sulfuric acid

Products = calcium sulfate, water, carbon dioxide gas

So the general form of an equation:


becomes the word equation:

calciumcarbonate

+ sulfuricacid

→ calciumsulfate

+ carbondioxide gas

+ water

This is much simpler than trying to explain the chemical reaction with sentences. However, word equations are still quite long.

calcium carbonate sulfuric acid watercalcium sulfate carbon dioxide

CaCO3 H2SO4 H2OCaSO4 CO2

+ + +

+ + ++ + +

The atoms from the calcium carbonate combine with the atoms from the sulfuric acid to produce calcium sulfate, hydrogen and carbon dioxide.

Figure 5.1.1

PEARSON science 10142


Scientists can write the equation much more effectively by replacing the chemical names with their chemical formulas. The chemical equation for the previous example then becomes:

CaCO3 + H

2SO

4 → CaSO

4 + CO

2 + H

2O

This type of chemical equation is known as a formula equation. The formula equation is shorter to write and contains more information. It shows exactly what atoms (or ions) are involved in the chemical reaction. Figure 5.1.1 shows how the reactants in the equation above rearrange to form the products.

Showing statesThe reactants and products in a chemical reaction can be in one of four states—solid, liquid, gas or aqueous solution (dissolved in water). Chemists give these states the symbols:

• (s) for a solid

• (l) for a liquid

• (g) for a gas

• (aq) for an aqueous solution.

The symbols can be added to the formula equations to give even more information about the chemical reaction. In the previous example, calcium carbonate and calcium sulfate are both solids, sulfuric acid is an aqueous solution, water is a liquid and carbon dioxide is a gas. All of this information can be included in the formula equation by writing the symbol for the state next to the formula name:

CaCO3(s) + H

2SO

4(aq) → CaSO

4(s) + H

2O(l) + CO

2(g)

The states are always written after the formula name in brackets.

Balanced chemical equationsThe formula equation for the reaction of calcium carbonate with sulfuric acid is a balanced equation. This means that it has the same number of atoms of each element on both sides of the equation. You can easily check this by counting the number of atoms in the reactants and products:

Reactants = 1 × Ca, 1 × C, 7 × O, 2 × H, 1 × S

Products = 1 × Ca, 1 × C, 7 × O, 2 × H, 1 × S

Balanced equations are consistent with the law of conservation of mass. This law states that:

During a chemical reaction, atoms cannot be created or destroyed.

You cannot create or destroy atoms in a chemical reaction. But you can rearrange them. As a result, the number of atoms in the reactants must equal the number of atoms in the products. Also, the mass of the reactants must equal the mass of the products. This is shown in Figure 5.1.2.

reactants products

The total mass of these beakers does not change despite a chemical reaction having taken place. The law of conservation of mass says that the total mass of the reactants and the total mass of the products must be the same.

Figure 5.1.2

However, not all formula equations will be balanced when you first write them. For example, when hydrogen gas reacts with oxygen gas, the product is water. The word and formula equations for this reaction are:

hydrogen + oxygen → water

H2(g) + O

2(g) → H

2O(l)

Counting the number of atoms on both sides of the equation shows that the equation is not balanced.

Reactants = 2 × H, 2 × O

Products = 2 × H, 1 × O

This means that if one molecule of hydrogen reacts with one molecule of oxygen, then an oxygen atom is left over. This is shown in Figure 5.1.3.

hydrogen gas oxygen gas water an oxygen atom

H2 O2 H2O O

+

++

+

++

A single hydrogen molecule will not react with a single oxygen molecule because there would be an extra oxygen atom left over.

Figure 5.1.3



However, if two hydrogen molecules react with one oxygen molecule, then the atoms can rearrange to produce two complete molecules of water. This is shown in Figure 5.1.4. Chemists represent this reaction as a balanced formula equation by writing:

2H2(g) + O

2(g) → 2H

2O(l)

Placing a 2 in front of the chemical formula for hydrogen and water indicates that the reaction uses two hydrogen molecules and produces two water molecules. Re-counting the number of atoms in the reactants and products shows that this equation is now balanced.

Reactants = 4 × H, 2 × O

Products = 4 × H, 2 × O

Consider another chemical reaction in which calcium metal (Ca) reacts with oxygen gas (O

2) to produce solid calcium

oxide (CaO). The reactants in this reaction are calcium and oxygen gas. The only product is calcium oxide. Therefore, the general equation:


becomes the word equation:

calcium + oxygen → calcium oxide

Replacing the chemical names with their formulas gives the formula equation:

Ca + O2 → CaO

Adding the states to the formula equation gives:

Ca(s) + O2(g) → CaO(s)

Checking the atoms of each element on both sides shows that the equation is unbalanced:

Reactants = 1 × Ca, 2 × O

Products = 1 × Ca, 1 × O

However, it will be balanced if two calcium atoms react with one oxygen molecule to produce two CaO molecules. So the final balanced equation can be written as:

2Ca(s) + O2(g) → 2CaO(s)

hydrogen gas oxygen gas water

2H2 O2 2H2O

+

++

It takes two hydrogen molecules for each oxygen molecule, and this produces two water molecules.Figure 5.1.4

Big burnersThe fuel tanks that supply fuel to power space rockets into orbit do not use petrol. Some use oxygen and hydrogen that react explosively to produce large amounts of energy.

The equation is:

2H2(g) + O2(g) → 2H2O(l)

This creates the enormous plume of exhaust gases that exit from the rocket motors. The rockets accelerate the massive weight to reach escape velocity of about 11 km/s.

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Balancing equationsBalancing chemical equations can be tricky, but if you follow some simple steps you should arrive at the right answer. Let’s look at the reaction between potassium carbonate (K2CO3) and nitric acid (HNO3), which produces potassium nitrate (KNO3), water (H2O) and carbon dioxide (CO2).

1 Write the word equation.

potassium carbonate + nitric acid → potassium nitrate + water + carbon dioxide

2 Write the unbalanced equation by replacing the chemical names with the chemical formulas.

K2CO3 + HNO3 → KNO3 + H2O + CO2

3 Balance each element one by one.

Potassium (K): There are two on the left and only one on the right, so put a 2 in front of the potassium nitrate (KNO3). This is sensible because you cannot destroy atoms—if you start with 2, you must end up with 2.

K2CO3 + HNO3 → 2KNO3 + H2O + CO2

Carbon (C): There is one on the left and one on the right, so you don’t need to change anything.

Oxygen (O): There are six on the left (three from the K2CO3 and three from the HNO3). However, there are nine on the right:

• 1 from the H2O

• 2 from the CO2

• 6 from the 2KNO3

Putting a 2 in front of the HNO3 solves the problem:

K2CO3 + 2HNO3 → 2KNO3 + H2O + CO2

Now everything balances. (Note that, when trying to balance by adding numbers, this adds multiple lots of everything in the formula. For example, adding a 2 in front of the K2CO3 would also balance the oxygen atoms but it would unbalance the potassium and carbon atoms.)

Hydrogen (H): There are now two on the left and two on the right, so this balances.

Nitrogen (N): There are now two on the left and two on the right, so this balances.

4 Double check the numbers of atoms on both sides of the equation.

Reactants = 2 × K, 1 × C, 9 × O, 2 × H, 2 × N

Products = 2 × K, 1 × C, 9 × O, 2 × H, 2 × N

The equation is now balanced.

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In the limelightSolid calcium oxide (CaO) is also known as lime or quicklime. When it is heated to 2500°C it begins to glow with an extremely bright light. For this reason, it was used in theatres for lighting before the discovery of electricity and is the origin of the term ‘in the limelight’.

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p148 5.1



5.2 Classifying chemical reactions

Decomposition reactionsWhen a single reactant breaks apart to form several products, the reactant is said to decompose. The general form of a decomposition reaction can be written as:

XY → X + Y

An everyday example of a decomposition reaction is the chemical reaction that puts the fizz in soft drinks like the one shown in Figure 5.2.1. Soft drinks contain dissolved carbonic acid (H

2CO

3). When carbonic acid decomposes, it forms water

(H2O) and bubbles of carbon dioxide gas (CO

2). The carbon

dioxide gas formed by this reaction remains dissolved in the soft drink until the lid is removed.

The balanced equation for the decomposition of carbonic acid is:

carbonic acid → water + carbon dioxide

H2CO

3(aq) → H

2O(l) + CO

2(g)

There are many different types or classes of chemical reactions. Each type of chemical reaction has something in common. This could be common reactants or products or the way that the chemical reaction takes place. Classifying chemical reactions helps chemists understand how chemical reactions work. By understanding how one chemical reaction works, scientists can understand more about all reactions of the same type.

The decomposition reaction of carbonic acid gives carbonated water its fizz.

Figure 5.2.1

carbon dioxide gas

149Chemical reactions


Thermal decompositionSome substances will only decompose when heated to high temperatures. This is known as thermal decomposition. Metal carbonates and metal hydrogen carbonates both undergo thermal decomposition.

Thermal decomposition of sodium azide (NaN3) is a chemical

reaction that saves lives every day by inflating vehicle airbags like the one in Figure 5.2.2. When sodium azide is heated, it decomposes into sodium metal and nitrogen gas. The balanced equation is:

sodium azide → sodium + nitrogen gas

2NaN3(s) → 2Na(s) + 3N

2(g)

Just 100 grams of sodium azide can produce around 56 litres of nitrogen gas in under 0.03 seconds. This reaction rapidly inflates the airbag in the event of a collision.

The decomposition of sodium azide (NaN3) saves lives every day.

Figure 5.2.2

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Combination reactionsCombination reactions occur when two reactants combine to form a single product. The general equation for a combination reaction can be written as:

X + Y → XY

Combination reactions are important in industry. For example, a combination reaction is used to create hydrochloric acid for industry and laboratories. First, hydrogen gas (H

2) and

chlorine gas (Cl2) are combined to form hydrogen chloride gas

(HCl) in large chemical plants like the one in Figure 5.2.3.

The balanced equation for the combination of hydrogen and chlorine is:

hydrogen gas + chlorine gas → hydrogen chloride gas

H2(g) + Cl

2(g) → 2HCl(g)

The hydrogen chloride gas that is produced is then bubbled through de-ionised water to produce hydrochloric acid.

Hydrochloric acid is manufactured at chemical plants using a combination reaction between hydrogen gas and chlorine gas.

Figure 5.2.3

Raisin lava lamp Can you create a lava lamp with a decomposition reaction?

Collect this …• clear fizzy drink such as lemonade or tonic water• raisins• clear glass or bottle

Do this …1 Pour the lemonade into the clear glass or bottle.

2 Add several raisins.

Record this …Describe what you saw.

Explain why you think this happened.

funscience



Precipitation reactionsOccasionally when two clear solutions are mixed together, they react to form a solid. The solid is said to precipitate out of the solution. As shown in Figure 5.2.4, most precipitates quickly fall to the bottom of the beaker. These types of reactions are known as precipitation reactions. For example, the scale that builds up in kettles, taps and pipes is solid calcium carbonate (CaCO

3) that has precipitated out of the tap water.

yellow precipitate

Precipitation reactions occur when two aqueous solutions react to produce a solid.

Figure 5.2.4

Precipitation reactions and solubilityA precipitation reaction occurs when two soluble reactants combine to form an insoluble product known as the precipitate. A substance is said to be soluble if it dissolves. For example, sugar is soluble in water. A substance is insoluble if it does not dissolve. For example, chalk is insoluble in water.

When a soluble substance is dissolved in water, the particles that make up the substance are spread thinly throughout the solution. The particles are so small and so thinly distributed that they cannot be seen with the naked eye. As a result, the solution appears transparent (clear, not cloudy or murky). It may be coloured like food colouring in water, but you can see through it clearly.

For example, when table salt or sodium chloride (NaCl) dissolves, it breaks apart into positive sodium ions (Na+) and negative chloride ions (Cl–) as shown in Figure 5.2.5. This is because table salt is an ionic compound.

Dissolved sodium and chloride ions are spread evenly throughout the solvent and are invisible to the eye.

solvent

sodium chloride (NaCl)crystal lattice

When sodium chloride dissolves, the lattice breaks apart and the ions distribute through the solution.

Figure 5.2.5

Ionic compoundsIonic compounds are crystalline substances that are made up of a crystal lattice of positive ions (cations) and negative ions (anions). Ionic compounds are usually hard, brittle and can be brightly coloured like the ones shown in Figure 5.2.6.

There are many different types of ionic compounds such as salts that come in a wide variety of colours.

Figure 5.2.6

Painful precipitatesYour body is full of dissolved compounds. However, sometimes these compounds precipitate out as hard deposits in the kidneys. These deposits, called kidney stones, are extremely painful. Usually kidney stones will pass out of the body with urine. However, in severe cases, the stones may have to be removed surgically or shattered by intense soundwaves.

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kidney stones



The cations that make up the crystal lattice are atoms (or groups of atoms) that have lost electrons and therefore have a positive charge. Anions are atoms (or groups of atoms) that have gained electrons and therefore have a negative charge. Table 5.2.1 lists common cations and anions.

Table 5.2.1 Common cations and anions

Chemical name Symbol

Cations

Lost 1 electron

Hydrogen ion H+

Lithium ion Li+

Sodium ion Na+

Potassium ion K+

Ammonium ion NH4+

Copper(I) ion Cu+

Lost 2 electrons

Calcium ion Ca2+

Magnesium ion Mg2+

Barium ion Ba2+

Copper(II) ion Cu2+

Iron(II) ion Fe2+

Lost 3 electrons

Iron(III) ion Fe3+

Aluminium ion Al3+

Anions

Gained 1 electron

Fluoride F–

Chloride Cl–

Bromide Br–

Iodide I–

Hydroxide OH–

Nitrate NO3–

Hydrogen carbonate HCO3–

Gained 2 electrons

Oxide O2–

Sulfide S2–

Sulfate SO42–

Carbonate CO32–

Gained 3 electrons

Nitride N3–

Phosphate PO43–

Naming ionic compoundsThe name of an ionic compound is simply the name of the cation together with the name of the anion. For example, barium sulfate (BaSO

4) is made up of the barium cation (Ba2+)

and the sulfate anion (SO4

2–). In the cases where an atom can have more than one type of ion (such as copper(I), Cu+, and copper(II), Cu2+), a roman numeral is included in the name of the compound. For example, copper(I) hydroxide (CuOH) or copper(II) sulfate (CuSO

4).

Ionic compounds are always charge neutral. This is represented in the chemical formula by ensuring that the total charge on the cations balances the total charge on the anions. For example, sodium oxide is made up of sodium ions (Na+) with a charge of +1 and oxide ions (O2–) with a charge of –2. Therefore, the symbol for sodium oxide is Na

2O. This formula

indicates that there needs to be two sodium ions for every oxide ion in the crystal lattice to balance the charge.

Polyatomic ions are ions with more than one atom. Examples are NH

4+ and SO

42–. The chemical symbol of these ions is put

inside brackets when more than one is needed for a balanced formula. For example, the chemical formula for calcium hydroxide is Ca(OH)

2. This indicates that there are two hydroxide

ions (OH–) to balance the charge of each calcium ion (Ca2+).

Predicting precipitation reactionsScientists use the solubility rules in Table 5.2.2 to predict if a precipitation reaction will occur when two ionic solutions are mixed.

Table 5.2.2 Solubility rules

Negative ions (anions)

Positive ions (cations)

Solubility of compounds

Acetate, CH3COO– All Soluble

All Li+, Na+, K+, Rb+, NH4+ Soluble

Chloride, Cl–

Bromide, Br–

Iodide, I–

Ag+, Pb2+, Hg2+, Cu+ Low solubility

All others Soluble

Hydroxide, OH–

Li+, Na+, K+, Rb+, NH4+,

Sr2+, Ba2+ Soluble

All others Low solubility

Nitrate, NO3– All Soluble

Phosphate, PO43–

Carbonate, CO32–

Li+, Na+, K+, Rb+, NH4+ Soluble


Sulfate, SO42–

Ca2+, Sr2+, Ba2+, Pb2+ Low solubility

All others Soluble

Sulfide, S2–

Li+, Na+, K+,Rb+, NH4+,

Be2+, Mg2+, Ca2+, Sr2+, Ba2+

Soluble


Using the solubility rules, it is possible to predict that a potassium chloride solution and a silver nitrate solution will react to form a silver chloride precipitate and leave behind a potassium nitrate solution (Figure 5.2.7). The balanced equation for this reaction is given by:

potassium chloride + silver

nitrate → potassium nitrate + silver

chloride

KCl(aq) + AgNO3(aq) → KNO

3(aq) + AgCl(s)

Silver chloride precipitates out as a white solid when potassium chloride is mixed with silver nitrate.

Figure 5.2.7

white silver chloride precipitate



The solubility rules state that all potassium ionic compounds are soluble and therefore potassium chloride (KCl) is soluble. The rules also state that all nitrates are soluble. Therefore, silver nitrate (AgNO

3) must be soluble. Together, these

solutions can combine to create potassium nitrate (KNO3)

and silver chloride (AgCl). Potassium nitrate (KNO3) must

Predicting precipitation reactionsIt is possible to predict the outcome of mixing two solutions by considering the solubility of all the possible combinations of cations and anions. Consider a mixture of solutions of magnesium sulfate (MgSO4) and barium nitrate (Ba(NO3)2).

Step 1: Swap the cations and anions of the reactants to get the possible products.

Product 1 = Magnesium nitrate (Mg(NO3)2)

Product 2 = Barium sulfate (BaSO4)

Step 2: Check the solubility of the possible products in Table 5.2.2.

Product 1 = Magnesium nitrate is soluble because all nitrates are soluble.

Product 2 = Barium sulfate is insoluble because all sulfates are soluble except Ba2+, Ca2+, Sr2+, Pb2+.

Step 3: Write the chemical equation for the reaction showing that barium sulfate is a solid precipitate.

barium nitrate solution + magnesium sulfate

solution → barium sulfate solid + magnesium nitrate

solution

Ba(NO3)2(aq) + MgSO4(aq) → BaSO4(s) + Mg(NO3)2(aq)

Combustion is a chemical reaction used every day to cook, provide warmth, run cars and produce electricity.

Figure 5.2.8

Oxidation and reduction reactionsOxidation and reduction reactions include a wide variety of reactions. However, it is not always obvious when an oxidation and reduction reaction has taken place.

Oxidation reactionsIf a substance combines with oxygen during a chemical reaction, then you can be sure that an oxidation reaction has occurred. Two familiar examples of oxidation reactions are combustion and corrosion.

During combustion reactions, substances burn rapidly in oxygen and produce large amounts of heat and light. Lighting a match, burning gas on a stove top, igniting fuel in car engines and burning coal in an electrical power station are all examples of combustion (Figure 5.2.8).

When methane gas is burnt in oxygen on a gas stove or Bunsen burner, the chemical combustion reaction is:

methane + oxygen → carbon dioxide + water

CH4(g) + 2O

2(g) → CO

2(g) + 2H

2O(l)

In this reaction, the methane is oxidised because it combines with oxygen in the air to form carbon dioxide and water. The oxygen is referred to as the oxidising agent because it has caused the methane to oxidise.

5.3

be soluble because all potassium ionic compounds and all nitrates are soluble. However, the solubility rules show that silver chloride is only slightly soluble in water and therefore it must precipitate out of the solution as a solid. Using these rules, scientists can predict the outcome of any precipitation reaction.

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Corrosion occurs when metals react with oxygen to form metal oxides. For example, when iron is exposed to oxygen in the presence of water, it forms rust or iron(III) oxide (Fe

2O

3). You

can see it in Figure 5.2.9. The equation for this reaction is:

iron + oxygen gas → iron(III) oxide

2Fe(s) + 3O2(g) → 2Fe

2O

3(s)

In this case, the iron metal is being oxidised and the oxygen gas is the oxidising agent.

Rust is the product of an oxidation reaction, more specifically called corrosion.

Figure 5.2.9

Reduction reactionsReduction reactions are the opposite of oxidation reactions. If a compound loses oxygen atoms, you can be sure a reduction reaction has taken place. For example, when copper oxide is heated to very high temperatures in the presence of carbon, the copper(II) oxide loses its oxygen and forms copper metal. The chemical equation for this reaction is:

copper(II) oxide + carbon → copper + carbon dioxide

2CuO (s) + C (s) → 2Cu (s) + CO2 (g)

Here, the copper oxide is reduced and carbon is the reducing agent. However, you could also say that the carbon is oxidised and that the copper(II) oxide is the oxidising agent. Oxidation and reduction reactions always occur in pairs. Therefore, they are commonly referred to as redox reactions.

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Redox reactions and electronsRedox reactions do not always involve oxygen. Redox reactions also include any chemical reaction where electrons are transferred from one substance to another substance. The substance that loses its electrons is said to be oxidised. The substance that gains the electrons is said to be reduced. An easy way to remember this is by the mnemonic OILRIG:

Oxidation Is Loss Reduction Is Gain

In short:

Oxidation is the gain of oxygen or the loss of electrons.

Reduction is the loss of oxygen or the gain of electrons.

Identifying redox reactions is not always easy. For example, precipitation reactions are not redox reactions. There is no exchange of electrons even though the charged ions in solution come together to form a crystal lattice. Similarly, neutralisation reactions between acids and bases also are not redox reactions because there is no exchange of electrons between atoms.

Metal displacement reactionsMetal displacement reactions are simple redox reactions that involve only the transfer of electrons from one metal atom to another. For example, when zinc metal is placed in a solution of copper sulfate, the zinc atoms form zinc ions (Zn2+) that dissolve into solution. At the same time, the copper(II) ions (Cu2+) form solid copper crystals on the zinc as shown in Figure 5.2.10. Here, the zinc is said to displace the copper from solution.

The chemical equations for this reaction are:

copper(II) ions + zinc → copper + zinc ions

Cu2+(aq) + Zn(s) → Cu(s) + Zn2+(aq)

Acrobatic flame Can a flame travel along candle fumes?

Collect this …• candle• box of matches

Do this …1 Light the candle

and let it burn for a couple of minutes.

2 Strike another match and then blow out the candle.

3 Put the flame of the lit match in the fumes coming from the unlit candle.

4 The candle should reignite as if by magic. See how far you can get the flame to jump.

Record this …Describe what you saw.Explain why you think this happened.

funscience

SAFETYBe very careful when using matches and candles. Be careful to blow matches out and rinse with water to make sure they are out before disposing of them.



Unit review5.2Remembering 1 List two examples each of combination, decomposition,

precipitation and redox reactions.

2 Name two metals that are:a nativeb extracted by carbon reductionc extracted by electrolysis.

3 Name a positive ion that is non-metallic.

4 List names and symbols of three polyatomic ions.

5 State whether nitrates are normally soluble or insoluble.

6 Name the following ionic compounds.a RbBr b K2

Sc BeO d Na

3N

e NH4Cl f LiOH

g Ag2CO

3 h ZnSO

4

Understanding 7 Explain why oxygen is written as O

2 in chemical reactions

rather than just O.

8 Explain why combination and decomposition reactions could be considered the reverse or opposite of each other.

9 Describe what happens when sodium ions come in contact with the negative electrode in a cell used for electrolysis.

10 Describe what observations may be made when a precipitation reaction occurs.

Applying 11 Identify a combination reaction that occurs in a blast

furnace.

12 Apply rules for formula writing to write the formula for calcium chloride.

13 Identify if the following reactions are combination, combustion or decomposition reactions.a 2KClO3

→ 2KCl + 3O2

b CH4 + 2O

2 → CO

2 + 2H

2O

c O2 + 2H

2O → 2H

2O

2

14 Use formula equations to rewrite the following word equations.a carbon + oxygen → carbon dioxideb copper(II) carbonate → copper(II) oxide + carbon

dioxidec propane (C

3H

8) + oxygen → carbon dioxide + water

15 Use word equations to rewrite the following formula equations.a 2Mg + O

2 → 2MgO

b 2H2O → 2H

2 + O

2

c CaO + H2O → Ca(OH)

2

16 Use Table 5.2.2 on page 152 to predict the precipitate formed when these solutions are mixed.a silver nitrate and sodium chlorideb mercury(II) nitrate and potassium iodidec calcium nitrate and lithium carbonated barium nitrate and sodium sulfate

17 Use word and formula equations to describe the following redox reactions.a aluminium corrodingb magnesium combusting in oxygen to form

magnesium oxidec magnesium metal displacing nickel ions from solution

Analysing 18 Discuss ways in which combustion is important in our

everyday lives.

19 Calculate the number of each type of atom in the following chemical formulas.a (NH

4)

2SO

4

b K2Cr

2O

7

c Ca(OH)2

Evaluating 20 Evaluate how learning to classify reactions into types has

helped you to better understand reactions.

Creating 21 Construct a table to summarise the different reaction

types in this unit. Use your own headings to help you clarify the typical reaction and examples.

Inquiring

1 Explain why the decomposition of mercury oxide (HgO) was a very important reaction for 18th-century chemists Carl Wil helm Scheele, Joseph P riestley and Antoine-Laurent Lavoisier.

2 Research the ingredients used in gun powder and how the chemical reaction works. Identify which reactants might be oxidizing agents and which might be reducing agents.

3 Research car airbags and find out what heats the sodium azide in a collision.

4 a Design an experiment to determine the contents of three unlabelled beakers, containing a solution of either sodium chloride, barium nitrate or potassium nitrate.

b Describe what you expect to observe.c Write balanced formula equations for each.



Documents

Chemical reactionssc130chc.weebly.com/uploads/7/1/6/9/71691711/ps10_10... · 2019. 11. 11. · 5.1Chemical equations Every time you light a candle, bake a cake, take a breath or even